Not sure if it's called "curves" in English, but what I am refering to is graphs that repeat over a given time. ie f(x) = sin(x) The problem I am having is understanding the following: Given: f(x) = sin(x) g(x) = cos(x) Find f(x) - g(x) by A(cos(x - x0)). Which gives: A(cos(x - x0)) = A(cos(x0))cos(x) + A(sin(x0))sin(x) A(cos(x0)) = 1 A(sin(x0)) = -1 thus: A = sqrt(1^2 + (-1)^2) = 1 Finding x0: tan wx0 = 1/(-1) 1*x0 = arctan(-1) x0 = -0.79 Here I'm pretty much lost. I've probably done some mistakes along the way as well :( What is -0.79? x0 is supposed to be the 'top' of the curve right? ie to find every top, you would have something like: x0 +/- |n|*2PI Where n is a whole number(1..inf) and 2PI would be the period of each "curve". Could someone explain this to me, I'm trying to learn this by just reading a book and I'm having a hard time.